Nearly two dozen people were sickened by a chemical spill at a recycling facility in Phoenix, Ariz., in the early morning of Sept. 18.

Emergency units were called to the Phoenix North Transfer Station and Materials Recovery Facility and the plant was evacuated. No serious injuries were reported but the source and the nature of the spill have still not been identified, local TV station 3TV reported.

Larry Nuòez of the Phoenix Fire Department told reporters that emergency units were handling "an airborne hazard" and that hazardous-materials crews were trying to identify the substance that had leaked on site. The facility will be thoroughly inspected before anyone is allowed to go back in, reports said.

According to Capt. Troy Caskey, also with the Phoenix Fire Department, 19 people had been treated for symptoms including vomiting, scratchy throats and burning noses. None of them were hospitalized.

3TV quoted Caskey explaining that when the fire department arrived at the scene there was an unidentified odor. Initially, there were reports of a chemical spill and this prompted the evacuation of the entire staff. Emergency units deemed the building safe and allowed workers to go back in but then four people became sick. After a second evacuation that followed, 15 more employees developed the symptoms, he explained.

The facility is used to separate waste from recyclables and has the capacity to handle about 4,000 tons of waste per day, 3TV said.